Thermal transmittance coefficient (U value)

The heat transfer coefficient (U value in W/m²K) is a measure of the heat loss through glazing. It indicates the amount of warmth passing through the facade element in the state of equilibrium per unit time, per unit area and per unit of the temperature difference between the two sides of the facade element. This means that the U value is a measure of how much heat output flows from warm to cold at a temperature difference of 1 K (Kelvin). 

Today's U-values are around 1.1 W / m²K (double heat insulation glass) and 0.6 W / m²K (triple heat insulation glass). It is always the case: The lower the U value, the better the heat insulation.

(Ug) U-Value:

The small g expresses that the value applies only to the glazing. The U-Value of insulating glass depends on the thermal insulation coating, the type of gas filling, the degree of gas filling and the gap between the panes.